(a) Field of the Invention
The present invention relates to a method and system for measuring a tilt angle that measure a tilt angle according to a lateral acceleration and a yaw rate while the vehicle is turning.
(b) Description of the Related Art
In general, a vehicle travels on an inclined traveling road at a tilted angle and the tilt angle may be used for various purposes. For example, to improve fuel consumption and determine a change in a speed pattern of the vehicle, a tilt angle of a road may be used. Further, a tilt angle may be used to prevent the vehicle from slipping backward upon starting. Furthermore, the tilt angle may be used for determination of a traveling path of a navigation device, a position control of the vehicle, fuel consumption improvement of the vehicle, and detection of real time energy consumption of the vehicle.
The tilt angle may be measured by various methods such as use of an atmospheric pressure sensor, an acceleration sensor, an electronic compass, or a gyro sensor, but an acceleration sensor is widely used.
Most acceleration sensors are a longitudinal acceleration sensor that measures longitudinal acceleration. The longitudinal acceleration sensor generally uses a piezoelectric sensor. The longitudinal acceleration sensor using a piezoelectric sensor has a long bar form, and when the piezoelectric sensor of the long bar form is bent by an acceleration force, the piezoelectric sensor outputs a voltage corresponding thereto. The voltage represents corresponding acceleration. Hereinafter, unless stated otherwise, an acceleration sensor indicates longitudinal acceleration.
An example of calculating a tilt angle using the acceleration sensor will be described with reference to FIG. 1.
An output signal value (long_accel_val) of the acceleration sensor and a tilt angle (θ) corresponding to the output signal value may be calculated by the following Equation 1.
      Ma    =          F      -              (                              F            aerodynamic                    +                      F            Rolling                    +                      F            Climbing                          )                  Ma    =          F      -              (                              F            aerodynamic                    +                      F            Rolling                    +                      Mg            ⁢                                                  ⁢            sin            ⁢                                                  ⁢            θ                          )                        F      -              (                              F            aerodynamic                    +                      F            Rolling                          )              =          M      ·              (                  a          +                      g            ⁢                                                  ⁢            sin            ⁢                                                  ⁢            θ                          )                        long_accel      ⁢      _val        =          a      +              g        ⁢                                  ⁢        sin        ⁢                                  ⁢        θ                        g      ⁢                          ⁢      sin      ⁢                          ⁢      θ        =                  long_accel        ⁢        _val            -      a                          sin        ⁢                                  ⁢        θ            ≅      θ        =                                        1            g                    ⁢                      (                                          long_accel                ⁢                _val                            -              a                        )                          ⁢                                  ∴        θ            =                        1          g                ⁢                  (                                    long_accel              ⁢              _val                        -            a                    )                    
Wherein, M is a vehicle mass, a is a traveling acceleration of a vehicle, g is a gravity acceleration, F is an output of the vehicle, Faerodynamic is air resistance of the vehicle, Frolling is rolling resistance of the vehicle, and Fclimbing is tilt resistance of the vehicle.
For example, a traveling acceleration (a) of the vehicle may be obtained by differentiating an output value of a vehicle speed sensor that detects a vehicle speed. To obtain traveling acceleration of the vehicle by differentiating an output value of the vehicle speed sensor is well known to a person of a common skill in the art and therefore a detailed description thereof will be omitted.
When an output value (long_accel_val) and the traveling acceleration (a) of the acceleration sensor are known, a tilt angle (θ) is calculated by Equation 1 above. In Equation 1, when there is no difference between the output value (long_accel_val) of the acceleration sensor and the traveling acceleration (a), it may be determined that the tilt angle is 0 and the road is substantially level.
However, when measuring a tilt angle using the acceleration sensor as described above while the vehicle is turning, a lateral acceleration and/or a yaw rate corresponding to turn of the vehicle may occur and thus there may be a difference between an output value of an actual acceleration sensor and an actual acceleration value and thus an accurate tilt angle may not measured. When there is a difference between the actual acceleration and an output of an acceleration sensor by an influence of lateral acceleration and a yaw rate occurring during turn of the vehicle, the measured tilt angle may decrease.
FIG. 2 is an exemplary graph illustrating a situation in which a vehicle performs a U-turn while the vehicle brakes on a level road. Referring to FIG. 2, when the vehicle performs a U-turn, as the lateral acceleration and the yaw rate occur corresponding to turn, a measured tilt angle may reduce by about 7-10%. When the tile angle reduces, a control device of a vehicle using a tilt angle may erroneously recognize the road as a level road and thus erroneously control the vehicle.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.